2-Substituted-2-oxazolines form a known class of compounds having many members and many utilities. The chemistry of such oxazolines has been summarized, for example, by Wiley et al., Chemical Reviews, Vol. 44, 447 (1949), by Seeliger et al., Angew. Chem. International Edition, Vol. 5, No. 10, 875 (1966), and by Frump, Chemical Reviews, Vol. 71, No. 5, 483 (1971). Patents on monomeric oxazolines have been classified by the U.S. Patent and Trademark Office under 260/307F.
One of the prior art processes for preparing 2-substituted-2-oxazolines is the cyclodehydration of N-(.beta.-hydroxyalkyl)carboxamides. This cyclodehydration occurs in vapor phase over alumina (U.S. Pat. No. 3,562,263 and Frump vide supra, page 485) and in liquid phase over certain salts of manganese, cobalt, rare earth metals, molybdenum and tungsten (U.S. Pat. No. 3,681,329 and U.S. Pat. No. 3,681,333). The latter two patents indicate that the cyclodehydration reaction is brought about by heating the hydroxyamide and catalyst together in a distillation apparatus from which the oxazoline product distills from the reaction mixture as it is formed along with the by-product water.
In another process, Ghera et al., J. Chem. Soc., Chem. Commun., No. 11, 639 (1972) teach that 2-substituted-2-oxazolines are prepared by heating N-(2-hydroxyalkyl)carboxamides in the presence of solid zinc acetate. Experimentally, the authors heated the carboxamide reactant with a ten-fold excess of powdered anhydrous zinc acetate in a glass tube under a constant flow of nitrogen and atmospheric pressure. This resulted in a formation of a 1:1 complex of oxazoline with zinc acetate which was isolated. The complexes were subsequently decomposed in a separate step into oxazolines by treatment with water or filtration through a Florisil column.